Quadraphonic augmentation system

ABSTRACT

A quadraphonic augmentation apparatus for use with a conventional stereophonic sound system comprises two rear accoustic transducers connected by a pair of frequency changing devices to the stereo system audio channels. The frequency changing devices irregularly shift the frequency and hence the phase of the audio signals, so that the in-phase left and right channel signals which impart a directional quality to the stereo sound are out of phase at the rear transducers. The resultant sound pattern resembles that of a concert hall, remarkably simulating the &#39;&#39;&#39;&#39;presence&#39;&#39;&#39;&#39; of a live performance. Preferably, each frequency changing device comprises a phase splitter driving a multi-segmented rotary capacitor having an eccentric pick-up plate driven at a varying rate. Each rear accoustic transducer may include a rotary drum to create additional phase shift effects in the low frequency range.

United States Patent 91 Sauvey et al.

[451 Get. 16, 1973 QUADRAPHONIC AUGMENTATION SYSTEM [75] Inventors: Donald R. Sauvey, La Canada; Paul H. Sharp, Sierra Madre, both of Calif.

[73] Assignee: Columbia Broadcasting System, Inc.,

New York, NY.

[22] Filed: Sept. 27, 1971 [21] Appl. No.: 183,845

[52] US. Cl. 179/1 GQ, 179/100.4 ST, 179/lO0.1 TD [51] Int. Cl H04r 5/04 [58] Field of Search 179/1 GP, 1 G, 1 D, 179/100.4 ST, 100.1 TD; 84/1.24

[56] References Cited UNITED STATES PATENTS 3,322,899 5/1967 Renwick 179/1 GP 3,372,225 3/1968 Leslie 84/1.24

3,315,760 4/1967 Schwender 181/27 A 3,176,072 3/1965 Novak 179/1 G 3,665,105 5/1972 Chowning 179/1 G OTHER PUBLICATIONS Sansui Advertisement for QS-l February 1971 Hi Fidelity Magazine.

Primary ExaminerKathleen l-l. Claffy Assistant Examiner-Thomas DAmico Attorney-Flam and Flam [5 7] ABSTRACT A quadraphonic augmentation apparatus for use with a conventional stereophonic sound system comprises two rear accoustic transducers connected by a pair of frequency changing devices to the stereo system audio channels. The frequency changing devices irregularly shift the frequency and hence the phase of the audio signals, so that the in-phase left and right channel signals which impart a directional quality to the stereo sound are out of phase at the rear transducers. The resultant sound pattern resembles that of a concert hall, remarkably simulating the presence of a live performance. Preferably, each frequency changing device comprises a phase splitter driving a multi-segmented rotary capacitor having an eccentric pick-up plate driven at a varying rate. Each rear accoustic transducer may include a rotary drum to create additional phase shift effects in the low frequency range.

2 Claims, 6 Drawing Figures 7 I80." {Q go" 1 V 9a 1 /5 i 27 24 I 4/ a, I

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2 Sheets-Sheet 8 -5/ 1 115 5 FREQUENCY 7 AN D c 7 5kHz CH GING EVI E I510. 5 F B I MOTOR FREQUENCY FREQUENCY CHANGlNG DEVICE CHAN6\NG DEv\cE IMEG QUADRAPHONIC AUGMENTATION SYSTEM BACKGROUND OF THE INVENTION l. Field of the Invention The present invention relates to an apparatus providing quadraphonic sound augmentation for an existing stereophonic sound system.

2. Description of the Prior Art In a concert hall environment, the audience perceives some sounds directly from the stage and other sound components indirectly upon reflection from the walls and ceiling of the hall. A listener is surrounded by the music. Stereophonic sound systems attempt to simulate such an auditorium ambiance by using two acoustic transducers to duplicate the in-phase components which impart a directional sense to the music. But such stereo systems cannot simulate the indirect sound components which converge from all directions and with continuously varying phase differences to create the presence of a live performance. Quadraphonic sound systems strive to achieve concert hall realism through the use of additional sound sources behind the listener.

Four-channel quadraphonic sound systems separately translate the sounds detected in different quandrants of an auditorium; accurate reproduction of both direct and indirect sound components is achieved. In the future, such four-channel systems no doubt will become increasingly popular, especially as coding and decoding techniques are developed to enable quadraphonic recording on discs and tapes which are compatible with existing stereo systems.

In the meanwhile, attempts have been made to augment existing stereophonic systems so as to recreate the ambiance ofa concert hall. One approach is merely to add two rear speakers in parallel with the respective left and right front speakers. This approach is unsatisfactory, since the sounds emanating from behind the listener are in phase with those produced by the front speakers. The left-right directional separation is emphasized, and the rear sounds do not simulate the complex sound reinforcement patterns resulting from reflections in an auditorium.

Another prior art approach is to utilize a third rear center speaker. The in-phase components of the left and right stereo channels are cancelled electronically, and the residual, out-of-phase components are used to drive the rear speaker. As noted, the in-phase right and left channel audio signals impart directionality to the reproduced stereophonic sound. When these are cancelled, the remaining out-of-phase signals presumably correspond to the reflected sound components present in an auditorium. However, listening tests indicate that music reproduced by such a system does not have concert hall realism.

In yet another prior art quadrasonic augmentation system a small amount of the audio signal present in each stereo channel is mixed into the other channel. The mixed signals are supplied to rear speakers. Alternatively, either the mixed or unaltered stereo signals supplied to the rear speakers are randomly phaseshifted. In one system the phase angle is established by the amplitude of the signal in that channel. The phase modulator includes a capacitor and a light sensitive resistor illuminated by a lamp modulated by the audio signal. The changing brightness of the lamp varies the angle of the introduced phase shift, which in no case is greater than 360. This limited phase shift is not sufficient to recreate realistically an auditorium ambiance.

An object of the present invention is to provide a quadraphonic augmentation apparatus for use with an existing stereo sound system and which provides sound reproduction with exceptional concert hall realism.

SUMMARY OF THE INVENTION To accomplish the foregoing objective, the inventive quadraphonic augmentation apparatus comprises a pair of accoustic transducers, together with frequency changing devices which electronically modify the stereo signals so as to produce a sound pattern which closely simulates a concert hall environment.

In a preferred embodiment, each frequency changing device comprises a phase splitter and a rotary capacitor which together function to shift irregularly the frequency of an audio signal. The left front aduio signal is supplied via such a frequency changing device to the right rear accoustic transducer, and the right front signal is supplied via a like device to the left rear transducer. The resultant sound pattern has a random, complex interference pattern typical of an auditorium. The rear accoustic transducers each comprise a set of speakers effective in different frequency ranges and driven via an appropriate crossover network. A rotary drum associated with the low frequency speaker introduces dynamic beat effects which enhance the sound realism. m LRIEF DESCRIPTION OF THE DRAWINGS A detailed description of the invention will be made with reference to the accompanying drawings, wherein like numerals designate corresponding elements in the several figures.

FIG. 1 is an electrical block diagram of a preferred embodiment of the inventive quadrasonic augmentation apparatus.

FIG. 2 is an electrical block diagram of a preferred embodiment of the frequency changing device and accoustic transducer used in one channel of the apparatus of FIG. 1; a like device and transducer may be used in the other channel.

FIGS. 3 and 4 show alternative arrangements of the frequency changing device and accoustic transducer in a single channel of the augmentation apparatus.

FIG. 5 is an electrical block diagram of an alternative quadraphonic augmentation system in which the rear speakers are not crossed" with the front speakers.

FIG. 6 is an electrical schematic diagram of a phase splitter which may be used with the frequency changing device of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS attributed to forms later described, unless such charac-' teristics obviously are inapplicable or unless specific exception is made.

Referring now to FIG. 1, there is shown a sound system 10 wherein an apparatus 11 in accordance with the present invention provides quadraphonic augmentation for a conventional stereophonic sound system 12. The stereo system 12 includes a source 13 providing a pair of audio signals via respective electrical channels 14, 15 to a left front acoustic transducer-l6 and a right front acoustic transducer 17. The source 13 may comprise, e.g., a conventional stereophonic record player and amplifier or an FM stereo receiver. Each acoustic transducer 16, 17 may comprise a single speaker or a 7 set of speakers covering d'ifferent'auido frequency ranges.

may be of the type shown in the U.S. Pat. No. 3,315,760 to Jacob Schwendener. Such a drum 36 advantageously ismounted on a vertical shaft 37 coaxial with the speaker 32 and is driven by a motor 38. The drum 36 includes an interior arcuate chamber which directs sound from the speaker 32 laterally outward The quadraphonic augmentation apparatus 11 incorthe signalprocessed thereby, by an irreqular or continuously varying degree. As a result, sound components which are inphase when reproduced by the front transducers 16, 17 are. out of phase (and differ slightly in frequency) when reproduced by the rear transducers 18, 18'. The resultant sound pattern, which'is characterized by complex, continuously varying phase relationships, remarkably simulates the ambiance of a concert hall.

The frequency changing device 19 (or 19) may be of the type disclosed in either of U.S. Pat. Nos. 3,25 l ,924 or 3,372,225 to Donald .1. Leslie. Such a frequency changing device 19a is shown in FIG. 2,.and utilizes a rotary capacitor 21 having four equiangularly arrayed stationary plates 22, 23, 24 and 25 driven respectively by signals differing in phase by.0, 90, 180 and 270 with respect to each other. These signals are supplied by aphase splitter 26 receiving as an input the audio signal from the channel 15. The capacitor 21 also includes a rotor plate 27 eccentrically mounted with respect to the center of the stationary plates 22 through 25. A motor and drive mechanism 28 rotate the plate 27 at a varying rate.

The output from the capacitor 21, present on a line 29 from the rotor plate 27, will differ in frequency from the channel 15 input signal by an amount determined by the rate of rotation of the plate 27. For example, if the plate 27 is rotated clockwise as viewed in FIG. 2 at two revolutions per second, an input signal of 440 Hz will be translated'into an output signal of 442 Hz. By driving the plate 27 at a continuously varying rate, the output signal on the line 29 will be shifted irregularly in frequency with respect to the signal from the channel 15. The variable rate drive mechanism 28 may be of the type shown in the above-mentioned U.S. Pat. No. 3,372,225 to Leslie.

The output of the frequency changing device 19a (FIG. 2) is supplied via an audio amplifier 31 to an acoustic transducer 17a having a low frequency speaker 32, a pair of midrange speakers each designated 33 and a high frequency speaker 34. A conventional crossover network 35 separates the audio frequency components to the speakers 32, 33 and 34.

Enhanced performance is achieved by providing the low frequency speaker 32 with a rotary drum 36, which through an opening or mouth. 36a at the periphery of the drum 36. Rotation of the drum 36 produces a changingspatial interference pattern. Theresultant low frequency beat effects seem to move through the room, giving an enhanced quality to the reproduced sound.

Advantageously audio signal components in the frequency range of from about 30 Hz to about 800 Hz may be supplied by the crossover network 35 to the speaker 32 equipped with a rotating drum 36.

A gangedswitch 41 disconnects .the frequency changing device 19a, and permits the rear acoustic transducer. 17a be driven directly by asignal supplied via a line 42. By connecting the line 42 to one channel 7 of a quadraphonic source, the switch 41 permits mode selection between quadraphonic augmentation or fourchannel operation.

In the embodiment of FIG. 3, the frequency changing device 19 receives only the signal components in the frequency range from about 200 Hz about 3kI-Iz. This is the frequency range within which a person best is able to perceive phase differences between audio signals. Frequency separation is facilitated byv a filter network 42receiving an input from the channel 15. The output of the frequency changing device 19 is supplied via an amplifier 43 to a pair of midrange speakers 44. The filter network 42 also provides a low frequency output via an amplifier 45 to a bass speaker 46 (which a may incorporate a rotary drum) and a high frequency output via anamplifier 47 to a tweeter 48.

An alternative embodiment is shown in FIG. 4, wherein only frequency components below about SkI-lz are supplied to the rear acoustic transducers. Thus the circuit includes a low pass filter 51 interposed between the channel 15 and the frequency changing device 19. The output of the device 19 is supplied via and audio amplifier 52 to an acoustic transducer 17a of the type l optimum concert hall ambiance. Stereo directionality is achieved between any pair of transducers, however right-left separation of the sound is deemphasized, the effect being that the listener is surrounded and encompassed by the sound. In the alternative sound system 10' of FIG. 6, the rear acoustic transducers 18, 18' are not crossed. The sound pattern created by the system 10 is more indicative of left-right separation; nevertheless, the system 10' still provides concert hall realism unmatched by any prior art quadraphonic augmentation system. 7

In FIG. 6 there is shown a phase splitter 26a which may be used in the frequency changing device 190 of FIG. 2. In this circuit, the input signal is directed via a line to the base of a transistor 61 the collector of which is connected to a positive voltage source via a resistor 62 and the emitter of which is connected to ground via a resistor 63. Driven by the emitter and collector of the transistor 61 is a symmetric pair of capacitor-resistor networks 64, 65 which provide the appropriately phased signals at the capacitor plates 22 through 25.

The four signals fed to the capacitor 21 are separated in phase by 90 over a relatively large frequency range. Moreover, the absolute phase shift of each signal varies as a function of frequency with respect to the audio signal supplied on the channel 15. Therefore, if musical notes at two frequencies are present, these will be phase shifted by different angular amounts. The effect is further to deemphasize the directional aspects of the sound radiated by the rear transducers 18, 18', thereby enhancing the sense of presence provided by the system l0.

Other variations of the invention will be apparent to those skilled in the art. For example, a portion of each channel signal may be mixed into the other channel prior to processing by the frequency changing devices. Arrangements of speakers and filters other than those illustrated may be used as the rear acoustic transducers. Only one or more than two frequency changing devices and rear acoustic transducers could be used instead of two as illustrated.

Thus there is disclosed a novel quadrasonic augmentation apparatus for use -with a conventional stereo sound system and which provides concert hall realism in the reproduction of stereophonic program material.

Intending to claim all novel, useful and unobvious features shown or described, we claim:

1. For use with a sound system having first and secnd acoustic transducers for reproduction of a pair of stereophonic audio signals provided respectively via left and right electrical channels, augmentation apparatus for augmented reproduction of said audio signals comprising:

third and fourth acoustic transducers spatially separated from said first and second acoustic transducers,

first and second frequency changing devices for continuously, irregulrly shifting the frequency of an audio signal, and

circuit means for suppling an audio signal derived from said left channel via said first frequency changing device to said third acoustic transducer and for suppling an audio signal derived from said right channel viasaid second frequency changing device to said fourth acoustic transducer, and wherein each frequency changing device comprises;

a phase splitter for deriving from the input audio signal components having progressively shifted phase angles,

rotational capacitor means including a plurality of spaced stator plates receiving said progressively phase shifted components and an eccentric, rotary pick-up plate driven at a varying rate and suppling as an output a signal shifted in frequency by an extent corresponding to said rate, the average frequency of said shifted signal being offset from the input audio signal by an amount corresponding to the average rotational rate of said pick-up plate, the pick-up plates of said first and second frequency changing devices being rotated at different varying rates,

each of said third and fourth acoustic transducers including a rotary sound channel for producing acoustic modulation effects which are superimposed on the average offset frequency introduced electrically by said frequency changing device, the sound pattern generated by said four acoustic transducers having randomly varying interference patterns whereby stationary standing waves effectively are eliminated, said sound recreating the presence of a live performance.

2. A quadraphonic augmentation system for use with a stereophonic sound reproduction system in which a conventional stereophonic pair of signals are reproduced by a first pair of acoustic transducers, comprising:

a pair of frequency changing devices, each device operating indepenedently of the other to introduce electrically an average frequency offset to a respective one of said pair of signals, the amount of frequency shift produced by each device being varied continuously and irregularly, and

a second pair of acoustic transducers connected respectively to reproduce said irregularly shifted, average frequency offset signals,

each transducer of said second pair including a rotary sound channel for producing acoustic modulation effects which are superimposed on said electrically introduced average offset frequency, the sound pattern generated by said four acoustic transducers having randomly varying interference patterns whereby stationary standing waves effectively are eliminated, said sound recreating the presence of a live performance.

t k IF 

1. For use with a sound system having first and second acoustic transducers for reproduction of a pair of stereophonic audio signals provided respectively via left and right electrical channels, augmentation apparatus for augmented reproduction of said audio signals comprising: third and fourth acoustic transducers spatially separated from said first and second acoustic transducers, first and second frequency changing devices for continuously, irregulrly shifting the frequency of an audio signal, and circuit means for suppling an audio signal derived from said left channel via said first frequency changing device to said third acoustic transducer and for suppling an audio signal derived from said right channel via said second frequency changing device to said fourth acoustic transducer, and wherein each frequency changing device comprises; a phase splitter for deriving from the input audio signal components having progressively shifted phase angles, rotational capacitor means including a plurality of spaced stator plates receiving said progressively phase shifted components and an eccentric, rotary pick-up plate driven at a varying rate and supplying as an output a signal shifted in frequency by an extent corresponding to said rate, the average frequency of said shifted signal being offset from the input audio signal by an amount corresponding to the average rotational rate of said pick-up plate, the pick-up plates of said first and second frequency changing devices being rotated at different varying rates, each of said third and fourth acoustic transducers including a rotary sound channel for producing acoustic modulation effects which are superimposed on the average offset frequency introduced electrically by said frequency changing device, the sound pattern generated by said four acoustic transducers having randomly varying interference patterns whereby stationary standing waves effectively are eliminated, said sound recreating the presence of a live performance.
 2. A quadraphonic augmentation system for use with a stereophonic sound reproduction system in which a conventional stereophonic pair of signals are reproduced by a first pair of acoustic transducers, comprising: a pair of frequency changing devices, each device operating independently of the other to introduce electrically an average frequency offset to a respective one of said pair of signals, the amount of frequency shift produced by each device being varied continuously and irregularly, and a second pair of acoustic transducers connected respectively to reproduce said irregularly shifted, average frequency offset signals, each transducer of said second pair including a rotary sound channel for producing acoustic modulation effects which are superimposed on said electrically introduced average offset frequency, the sound pattern generated by said four acoustic transducers having randomly varying interference patterns whereby stationary standing waves effectively are eliminated, said sound recreating the pResence of a live performance. 